Now we’ll check out driving techniques that you can adopt to reduce your fuel
bill.

Drive Smoothly

Watching the road ahead is one of the key aspects of driving smoothly.

By watching the road a generous distance ahead you have more time to react to
changing traffic conditions such as traffic lights. This means you can ease
off the accelerator early, coast toward the lights and gently apply the brake to
wipe off the remaining vehicle momentum. This is by far the most fuel-efficient
way to drive.

In addition to watching the road ahead, it’s important to maintain a generous
distance to the car in front. All too often, drivers follow too closely,
which causes them to drive with on/off movements of the accelerator and so use excess fuel. If you watch the road ahead and
leave a considerable distance to the car in front, you can identify any lane
obstructions and have plenty of time to merge into another lane with the
flow of traffic. This technique means you’ll avoid getting stuck behind buses,
turning vehicles and collisions.

Accelerate with the smallest possible amount of throttle and ensure throttle
application is gradual. You should also begin feathering the throttle well
before you arrive at your desired speed – if you lift off when you arrive at
your desired speed you’re wasting fuel.

On the open road you should use the car’s cruise control (where fitted) to
ensure steady speed and fuel consumption. However, cruise control does not
necessarily give optimal fuel consumption in hilly terrain. A
more economical approach is to maintain constant throttle position and allow
some variation of road speed.

Use Low Engine Revs

Fuel consumption increases as a function of engine speed (rpm).

If you drive a car with a manual gearbox you can change up through the gears
at relatively low revs. The revs at which you should up-shift varies from
vehicle to vehicle but, as a rule, you should not need to exceed an engine speed
that’s half the redline. For example, if you’re driving a car with a 7000 rpm
redline you should avoid exceeding 3500 rpm. (But note that engines with poor
low-speed torque may require higher revs.)

If you drive a car with an automatic transmission, you can encourage low rpm
up-changes by gentle, smooth application of the throttle. Experiment with
different throttle positions and rates of throttle application to find the
driving style that causes the transmission to change up gears as
early as possible.

Reduce Idle Time

The longer your car’s engine idles, the more fuel you waste.

Prolonged idling in traffic is responsible for a considerable amount of city
fuel consumption. Wherever safely possible, you should switch off the engine to
halt unnecessary fuel consumption. Starting and stopping the
engine increases engine wear, but the effect is negligible once the engine is up
to normal operating temperature.

The practice of ‘warming up the engine’ before driving wastes fuel. A more fuel-efficient alternative is to drive the car gently (at light throttle and low revs) for the first few kilometres.

Many owners of turbocharged cars are guilty of wasting fuel during
unnecessarily long idle-down periods. Vehicle manufacturers typically fit an
in-cabin warning sticker that suggests a specific idle-down period – for
example, a Mitsubishi Galant VR4 has a sticker that suggests idling the engine
for 60 seconds immediately after operating at high speed or under heavy load.
This is ample time to cool down. Idle time can be
significantly reduced by driving conservatively for a minute or two before
stopping. If you drive conservatively well before stopping, you can safely reduce
your idle time to a handful of seconds. That’s the best way to do it.

Putting these Techniques to the
Test

To demonstrate the benefit of these driving techniques, we did a back-to-back
fuel consumption test in a 1.8 litre turbo Nissan 180SX automatic. The test
resembled the official UN ECE R101 test procedure with about 30 percent
open-road driving and the remaining 70 percent a mixture of urban and city
driving. The engine was switched off and started 3 times during the test. Each
of our 200km test loops began with a cold engine and with near-identical weather
and traffic conditions.

The first test was done with a ‘normal’ driving style – not looking a long
way ahead, jerky acceleration and braking and with a one minute idle-down for
each switch-off. The result of this test was an average fuel consumption of 9.75
litres per 100km.

The second test was done with a smooth driving style and a 20 second
idle-down for each switch-off. The result? An average consumption of 9.0 litres
per 100km – an improvement of 8 percent.

Not a bad saving for simply using a bit of nous...

Minimise Use of Air
Conditioning

In slow moving traffic, an air conditioner keeps vehicle occupants much
cooler than winding down the windows. It would be silly to suggest not using the
air conditioning, but you can make a fuel saving by occasionally switching it
off or setting the cabin temperature somewhere above ‘Max Cold’.

At a higher road speed it’s not clear-cut whether it’s more fuel efficient to
use the air conditioning or wind down the windows. We have seen conflicting
information on what’s the most efficient approach. We imagine results will vary
depending on vehicle aerodynamics, the power consumption of the air compressor
and many other variables. Why not perform your own testing as part of your daily
driving?

Smart Vehicle Usage

You can save a very significant amount of money just by planning your vehicle
use.

If you have a number of appointments and errands for the day, it’s best to
schedule them in one trip rather than several trips. Don’t be caught in the
situation where you need to drive to the local shops because you forgot to buy a
drink...

Also consider the time of your trip. Wherever possible, try to avoid
peak-hour traffic and major social events. Heavy traffic conditions are killers
for fuel economy.

In Part Four – the final - of this series we’ll take a look at aftermarket
vehicle modifications that enhance fuel economy...

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